A paving machine typically comprises a tractor or towing vehicle that moves ahead of a screed over a subgrade to be paved. The screed is a steel plate that has a two-dimensional slope that controls the contour of the finished pavement surface. The paving machine deposits a layer of asphalt or other paving material on the subgrade, and the thickness and contour of the asphalt layer are determined by a “floating” screed that is towed behind the towing vehicle. The screed smooths the top surface of the layer of the paving material, while at the same time controlling the vertical position of this surface and the thickness of the asphalt layer.
A paving machine deposits the paving material on the subgrade so that the top surface of the paving material follows a desired elevation contour. In some instances, the top surface of the asphalt is contoured in relation to an adjacent reference surface. In other cases, the asphalt is contoured to match a reference set by a surveyor. In all of these instances, it is necessary that the vertical position of the top surface of the deposited paving material be controlled precisely with respect to a reference of some sort, and this requires that the tow points of the tow arms be controlled with precision.
In other paving operations, the desired contour of the paved surface is defined in a three dimensional database, and the location of the paver, including the screed, is monitored by means of GPS receivers, laser receivers, automated total station systems, or similar systems. In these cases, the paver is operated to deposit a layer of paving material which matches in contour and thickness the parameters defined in the database.
Current paving technology that relies on the use of a screed can lead to variations in the thickness of deposited paving materials in comparison to the desired finished condition of the pavement. During deposition, paving materials can be smoothed by the screed to create a leveled surface. However, when compressible paving materials such as asphalt are subsequently compacted, the resulting pavement surface deforms and conforms to the profile of the underlying subgrade. Therefore, if surface defects and abnormalities such as depressions and humps exist in the subgrade, the same imperfections can be observed on the finished pavement, and can result in the formation of damaging structures such as potholes and bird bath. Furthermore, pooling water due to a lack of drainage on the surface of pavement having such defects can accelerate the damage of the pavements.
While the current state of the art allows precise evaluation of road surface topography, there still remains a need for optimizing the paving process such that surface defects can be minimized without incurring substantial engineering and reconstruction expenses.